No one likes to walk into work after just a few fitful hours of
sleep. But now there's evidence that not getting enough sleep may have
more serious consequences than dark circles under your eyes the next
morning. Researchers at the University of Chicago report in the Journal of the American Medical Association that too little sleep
can promote calcium buildup in the heart arteries, leading to the
plaques that can then break apart and cause heart attacks and strokes.

The University of Chicago team documented for the first time exactly
how much of a risk shortened shut-eye can be — one hour less on average
each night can increase coronary calcium by 16%. Among a group of 495
men and women aged 35 to 47, 27% of those getting less than five hours
of sleep each night showed plaque in their heart vessels, while 11% of
those sleeping the recommended five to seven hours did, and only 6% of
subjects sleeping more than seven hours each night showed such
atherosclerosis. "We were surprised by the findings," says Diane
Lauderdale, a professor of health studies at the University of Chicago
and lead author of the study. "We really were not expecting to find an
association at all, and certainly not one that was this strong." (See the Top 10 Medical Breakthroughs of 2008.)

Lauderdale and her team had reason to be skeptical. While the connection between sleep and heart disease
is of growing interest to researchers, earlier studies had been
inconclusive, and plagued by biases, including the fact that most of the
trials relied on people's self-reported accounts of their sleeping
habits. The scientists knew that teasing apart the myriad processes that
contribute to sleep, and then drawing scientifically sound connections
between them and the host of things that can trigger heart disease,
would be difficult at best. So the Chicago team isolated the most common
confounding variables that could explain both poor sleep and heart
problems, such as smoking, alcohol, and other medical conditions, and
also found a way to record, as accurately as possible, the amount of
sleep that the subjects got each night. Each volunteer wore a wrist
monitor that measured and recorded activity at 30 second intervals; when
the monitor was quiet, the subject was asleep.

While Lauderdale acknowledges that her results are far from the last
word on sleep and heart disease, the study does suggest that doctors and
patients should consider sleep in addition to the more familiar hazards
for the heart such as high cholesterol, hypertension and diabetes.
In Lauderdale's analysis, one additional hour of sleep was equivalent
to lowering systolic blood pressure by 16.5mm Hg. "We have enough
evidence from this study and others to show that it is important to
include sleep in any discussion of heart disease," says Dr. Tracy
Stevens, spokesperson for the American Heart Association and a
cardiologist at Saint Luke's Mid-America Heart Institute. "We talk about
the traditional risk factors, and now the other important thing we need
to include is sleep." (See pictures of how animals sleep.)

Exactly how a lack of sleep is feeding plaque in the heart arteries
isn't yet clear, but one explanation may involve inflammation. Too
little sleep can raise cortisol levels,
which fuels inflammation that can destabilize plaques. Once these
deposits rupture, they can block vessels in the heart or brain, causing a
heart attack or stroke. While the Chicago team did not track levels of
cortisol to test this theory, future studies might.

A simpler explanation might involve blood pressure.
In general, blood pressure dips during sleep, and over a 24 hour
period, people sleeping less will have shorter periods of lower blood
pressure, thus increasing their tendency to dislodge any unstable
plaques.

Whatever the reason might be, the results of this study make it clear
that sleep isn't just for dreamers. Getting enough sleep might just
save your heart.